The aforesaid lighting devices are used in the entertainment industry to obtain scenographic effects with play of lights produced by light beams. The entertainment industry is constantly searching for new plays of light. To this purpose, a modification of shape, orientation and colouring of the light beam by means of optical systems treating the light beam is already known. These optical systems are based on different principles and have different technical characteristics and potential. However, the current optical systems for treating light beams share a common need of heavy and bulky structural elements, which make more difficult the handling, the installation and the transportation of the optical lighting devices.